The present invention relates to an arrangement for automatically changing the transmission ratio of a speed-change gearbox arranged downstream of a drive engine in a power train of a motor vehicle to provide a changing-up to a higher gear, comprising an electronic control unit that forms a changing-up signal as a function both of a load of the drive engine and of a driving speed of the motor vehicle and an electro-hydraulic changing device connected by a changing-up line to the electronic control unit and receiving from the electronic control unit the changing-up signal. A first switch is arranged in the changing-up line that prevents the changing-up by setting a bistable multivibrator, the first switch being opened when the changing-up signal is present. A bistable multivibrator having a setting input and a resetting input is provided and is coupled to the first switch. A detection stage responsive to a change in level of an inhibiting signal is provided for preventing the changing-up and outputting a signal for setting the bistable multivibrator. The resetting input of the bistable multivibrator for a re-authorization of the changing-up is provided, by closure of the first switch, with a signal which corresponds to a significant position of an accelerator pedal and which is output when the accelerator pedal has been actuated into the significant position after the setting of the bistable multivibrator. A displacement transducer is controllably connected to an accelerator pedal and coupled to the resetting input of the bistable multivibrator. A threshold value stage is coupled between the displacement transducer and the resetting input, the threshold value stage determining the significant position. A delay element which is switchable on in response to the changing-up signal is coupled to a second switch that is arranged with the switch drivable by the bistable multivibrator in series with the changing-up line, the delay element during its delay time driving the second switch in an opening direction.
In a known arrangement of this kind 10 (DE 27 38 914 C2), the inhibiting signal for setting the bistable multivibrator, and thus for preventing changing-up of a step-by-step variable transmission, is triggered by quickly releasing the accelerator pedal. The threshold value stage for determining the significant position of the accelerator pedal at which the signal for resetting the bistable multivibrator (and thus for re-authorizing changing-up) is output, has a constant threshold value so that the significant position is the same for all changing-up operations and in all driving states. These driving states must be simply travelled through, by simply pressing down the accelerator pedal, in order to trigger the signal for the re-authorization of the changing-up by resetting the bistable multivibrator.
In contrast with the above, the object upon which the invention is based is essentially to orient the conditions for the re-authorization of the change in transmission ratio with the effect of changing-up, irrespective of how and with which parameters the inhibiting signal for preventing the change in transmission ratio has been formed, more towards the intentions of the driver with respect to changing-over of the gears during driving. Since if the driver does not intend to trigger a change in the transmission ratio with the effect of changing-up when he rapidly releases the accelerator pedal, a subsequent pressing down of the accelerator pedal cannot necessarily be taken to imply that the driver desires the opposite.
This and other objects are achieved by the present invention which provides an arrangement for automatically changing the transmission ratio of a speed-change gearbox arranged downstream of a drive engine in a power train of a motor vehicle to provide a changing-up to a higher gear, comprising an electronic control unit that forms a changing-up signal as a function both of a load of the drive engine and of a driving speed of the motor vehicle and an electro-hydraulic changing device connected by a changing-up line to the electronic control unit and receiving from the electronic control unit the changing-up signal. A first switch is arranged in the changing-up line that prevents the changing-up by setting a bistable multivibrator, the first switch being opened when the changing-up signal is present. A bistable multivibrator having a setting input and a resetting input is provided and is coupled to the first switch. A detection stage responsive to a change in level of an inhibiting signal is provided for preventing the changing-up and outputting a signal for setting the bistable multivibrator. The resetting input of the bistable multivibrator for a reauthorization of the changing-up is provided, by closure of the first switch, with a signal which corresponds to a significant position of an accelerator pedal and which is output when the accelerator pedal has been actuated into the significant position after the setting of the bistable multivibrator. A displacement transducer is controllably connected to an accelerator pedal and coupled to the resetting input of the bistable multivibrator. A threshold value stage is coupled between the displacement transducer and the resetting input, the threshold value stage determining the significant position. A delay element which is switchable on in response to the changing-up signal is coupled to a second switch that is arranged with the switch drivable by the bistable multivibrator in series with the changing-up line, the delay element during its delay time driving the second switch in an opening direction. The threshold value stage has a threshold value which is variable as a function of the position of the accelerator pedal and is settable to a constant offset above an instantaneous position of the accelerator pedal and is lockable onto when the delay element is switched on, so that the significant position merely deviates by the constant offset from an instantaneous position in which the accelerator pedal was located when the second switch opens. The second switch is additionally drivable by a first delay device which operates as a function both of the delay element and of the threshold value stage in such a way that the second switch remains opened over a delay time determined by the first delay device when the signal corresponding to the significant position occurs and switches on the first delay device.
In the arrangement according to the invention, the significant position of the accelerator pedal for re-authorizing the change in transmission ratio with the effect of changing-up is not the same for all changes in transmission ratio with the effect of changing-up and for all driving states but is always dependent (specifically varying by a constant offset) from that position in which the accelerator pedal was located when there was a change in level of the inhibiting signal for preventing the change in transmission ratio with the effect of changing-up. However, in this case, merely moving this significant position for re-authorization of the change in transmission ratio with the effect of changing-up is not sufficient, but rather the change in transmission ratio with the effect of changing-up remains initially inhibited for a predetermined delay time. Additionally, for a specific time period which is determined by the delay device which contains the threshold value stage for the significant accelerator pedal position, the switch in the changing-up line, which switch is driven by the delay element, remains open and thus at the same time prevents the change in transmission ratio with the effect of changing-up. If an inhibiting signal which again prevents the change in transmission ratio with the effect of changing-up does not occur within the delay time, the change in transmission ratio with the effect of changing up is authorized again after the delay time has elapsed.
In certain embodiments of the invention, the re-authorization of the change in transmission ratio with the effect of changing-up is associated with the condition that the driver keeps the accelerator pedal in a constant position or slightly releases the accelerator pedal, that is to say does not accelerate and thus indicates that he wishes to maintain the current driving speed. Thus, in the entire region above the respective changing-up line of the gear-change program, a change in transmission ratio with the effect of changing-up is also prevented from being carried out while the driver is accelerating.
In certain embodiments of the invention, one and the same monostable multivibrator is used in conjunction with a J-K master-slave multivibrator to determine the delay time of the delay element which can be switched on as a function of the changing-up signal, to determine the delay time of the delay device which contains the threshold value stage for resetting the bistable multivibrator, and to determine the delay time for the delay device which contains the detection stage for the direction of movement of the accelerator pedal.
In certain embodiments of the invention, the locking onto the threshold value which determines the significant position of the accelerator pedal for re-authorization is maintained for positive movements having the effect of an increase in power but can be cancelled in the case of negative movements having the effect that the threshold value is follow-up controlled downwards when the accelerator pedal is released. In such a driving state, the signal for the re-authorization of the change in transmission ratio with the effect of changing up is accordingly triggered, but the change in transmission ratio with the effect of changing-up itself is not triggered, when the driver slightly accelerates, as a result of which, however, the delay time of the monostable multivibrator, and thus the interrupting of the changing-up line, is triggered or extended.
An embodiment of the arrangement according to the invention which is advantageous in terms of circuit technology, for cancelling the locking onto, and follow up control of, the threshold value is also provided.
An embodiment, which is advantageous in terms of circuit technology, for locking onto the threshold value allowing for the restrictive actuation of the accelerator pedal in the arrangement according to the invention is provided.
An embodiment, which is advantageous in terms of circuit technology, of the arrangement according to the invention uses one and the same monostable multivibrator for determining the delay time of the delay element which is influenced by the changing-up signal, the delay time of the delay device which contains the threshold value stage for the re-authorization, and the delay time of the delay device which contains the detection stage for the direction of movement of the accelerator pedal is provided.
An advantageous embodiment of the arrangement according to the invention in which the inhibiting signal for setting the bistable multivibrator is not formed as a function of a rapid release of the accelerator pedal is provided.
An advantageous embodiment of the arrangement according to the invention in which the inhibiting signal for setting the bistable multivibrator is triggered as a function of a rapid release of the accelerator pedal is provided.
The invention can be applied, for example, both in speed-change gearboxes with step-by-step change of the transmission ratio and also in speed-change gearboxes with infinitely variable change of the transmission ratio.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.